The goal of the proposed work is to obtain fundamental biophysical data, principally thermodynamic, about the interactions of a set of eukaryotic DNA binding proteins with several forms of DNA. The proteins we will study are the higher molecular weight members of the so-called high mobility group nonhistone chromatin proteins, HMG-1, HMG-2, and HMG-E. The proteins will be isolated from nuclei of chicken red blood cells. We will study the interactions of all three proteins with DNA, but we will give special emphasis to HMG-E, a protein that is particularly abundant in mature avaian erythrocytes and that might play an important role in the development of those cells. HMG-3, a trypsin digestion product of HMG-E with altered DNA binding properties, will also be studied. We will determine binding site sizes for the interactions of each of the four proteins with both single-stranded and double-stranded DNA's, intrinsic association constants, and estimates of binding cooperativity. We will also study the effect of the proteins' binding on the conformation of DNA. The basic approaches in our work will be several sorts of sedimentation of protein/DNA mixtures and fluorescence titrations of proteins with DNA.